Frequency spectrum allocation to mobile network operators is traditionally done in fixed an exclusive manner by government authorities. This often results in poor spectral efficiency as co-located network operators may have different spectrum needs over time and space depending on the distribution and mobility of the respective users and their traffic demand.
Spectrum sharing and dynamic spectrum allocation to mobile network operators have been advocated as a key feature to improve spectral efficiency already by the WINNER project for cognitive radio systems and radio access networks beyond 3G. Spectrum sharing and dynamic spectrum allocation have found renewed interest for future wireless communication systems, which are expected to enable new services and business opportunities for emerging stakeholders, leading to a large number of mobile network operators with co-located network deployments that cannot be accommodated by traditional static spectrum allocation rule is employed.
There are various alternative technologies related to spectrum sharing. One solution is to employ a Common Radio Resource Manager (CRRM) entity governing the spectrum usage of networks participating in spectrum sharing. This approach, often referred to as vertical sharing, requires the networks to share information related to the availability and usage of the respective radio resources such as transmission time, load, etc.
A drawback of the CRRM approach is that network operators sharing spectrum are required to share valuable (in some cases confidential) information of their networks. Additionally, the amount of signalling required to and from the CRRM may become significant depending on the spectrum sharing algorithm employed.
With a horizontal approach, network operators sharing spectrum obey pre-defined rules to trade, share or compete for spectrum resources without a common radio resource manager.
Another approach is to utilize geo-location databases (GLDB) to inform all network operators sharing spectrum about the free spectrum resources in a particular location. The database should incorporate information on sharing rules determined by the local spectrum administrator.
A drawback of solutions for horizontal spectrum sharing and GLDBs is that the rules for the co-existence are typically very general, causing the algorithm to converge to sub-optimal solutions compared to the CRRM approach with lower spectral efficiency.
Additionally, conventional solutions for dynamic spectrum sharing/allocation among co-located communication systems do not address the particular characteristic of ultra-dense network. In particular, in ultra-dense networks, the coupling between spectral efficiency and deployed network density can be exploited to optimize the trade-off between spectrum allocation and utilized network density in order to support a certain traffic demand.